1. Field of the Invention
The present invention relates to poppet valves for internal combustion engines. These valves are used for the purpose of allowing either air, or air and fuel into the engine cylinders (intake valves) and for allowing spent gases to be removed from the cylinders (exhaust valves).
2. Disclosure Information
Poppet valves are used as described above to govern the flow of gases into and out of engine cylinders; these valves must seal tightly for a variety of reasons. First, in the event that the exhaust valves do not seal tightly, e.g., if the valve's head is either not placed tightly in contact with the valve's seat, or if the seat or valve are burned or otherwise eroded, unburned hydrocarbon emissions from the engine may be excessive. Further, if exhaust valves do not seal tightly the valve may become burned, causing a loss of engine compression, performance, fuel economy, and increased emissions.
Intake valves must also be sealed tightly to avoid problems with loss of compression and resultant loss of efficiency and power output. The trend toward multi-valve engines has exacerbated the problem of achieving adequate valve sealing because smaller valve stems must be housed within increasingly smaller valve guides, and this causes difficult machining issues in production plants because very small valve guide bores must be machined at a rapid pace using very small tooling. U.S. Pat. No. 5,313,917 (Santi) attempts to address the problem of valve sealing by providing a self-aligning valve having a relatively large gap between the valve guide bore and the valve stem, which is combined with an exceedingly short bushing located only in the vicinity of the port. Unfortunately, it is believed that such an arrangement would not work well with a modern automotive engine, because the small bushing used to seal the valve stem would need to be compliant enough to allow misalignment of the valve but yet function as a seal, which would be very difficult and likely not occur properly. In contrast, according to the present invention the valve guide, as opposed to the merely the valve is self-aligning. As a result, a system according to the present invention provides the advantage that the valve will be allowed to seal properly with its mating seat while at the same time the valve is properly supported within a valve guide having conventional length and sealing capability, so as to preclude the excessive loss of lubricating oil through the valve guide. This is a potential problem with the system shown in the '917 patent.
Those skilled in the art will appreciate that the avoidance of lubricating oil consumption by automotive engines is desirable inasmuch as the combustion products of lubricating oil have been implicated in the poisoning of automotive exhaust aftertreatment catalysts. As a result, the system of the '917 patent would not be expected to perform properly for this additional reason. In contradistinction, a system according to the present invention will provide proper oil control while at the same time promoting proper sealing between the valve head and the valve guide. Other advantages of the present invention will become apparent to the reader of this specification.